1. Field of the Invention
The present invention relates to a method of producing a color filter which is used in color liquid crystal displays, color scanners, and solid image pick-up elements and, more particularly, to a method of producing a color filter having excellent durability, suited for use which requires the durability after passing through the step of forming a pattern by means of an ink-jet printing method.
2. Description of Related Art
Examples of radiation-polymerizable colored compositions using coloring materials such as pigments and dyes known to date are (i) photo-curable colored compositions obtained by adding a photopolymerizable monomer and a photopolymerization initiator to a colored composition in which a coloring material is dispersed or dissolved in a binder resin solution and (ii) thermosetting colored compositions obtained by dispersing or dissolving a coloring material in a thermosetting resin. There has also been known a method of forming a colored image by a method of coating the colored composition on a substrate using an ink-jet printing method to form colored patterns and exposing the coated substrate to light or heat energy, thereby to fix the colored patterns. Examples of industrial application of these radiation-polymerizable colored compositions include color filters used in color liquid crystal displays, color scanners, and solid image pick-up elements.
The color filter is formed by arranging coloring materials on each pixel to selectively transmit three primary colors of light (e.g. red, green, and blue) or to selectively reflect three primary colors (e.g. cyan, magenta, and yellow), on a transparent substrate provided with a black matrix.
As the method of forming the color filter, a photolithography method, an electrodeposition method, a printing method, and an ink-jet printing method are known and the photolithography method is mainly used at present. This method is a method comprising many steps, wherein the three steps of applying a photopolymerizable colored composition to a substrate, exposing the substrate to radiation energy through a pattern-mask, and dissolving the non-required portion, and washing are repeated for each red, green, and blue pixels or each cyan, magenta, and yellow pixels, thereby to form a color filter. On the other hand, the ink-jet printing method, which can form red, green, and blue or cyan, magenta, and yellow pixels in one step, has received much attention because of its low cost due to the small number of steps.
Although methods of forming a color filter by the ink-jet printing method are disclosed in Japanese Unexamined Patent Application, First Publication No. Sho 59-75205, Japanese Unexamined Patent Application, First Publication No. Sho 61-245106, and Japanese Unexamined Patent Application, First Publication No. Sho 63-2945 03, the color filters obtained by these methods are inferior in heat resistance and solvent resistance because the coloring material consists of a dye. On the other hand, various methods using a resin and a pigment have been proposed as the method of producing a colored layer having excellent heat resistance and solvent resistance. For example, Japanese Unexamined Patent Application, First Publication No. Hei 5-224007 discloses a color filter using ink-jet printing ink comprising a melamine resin and a colorant; Japanese Unexamined Patent Application, First Publication No. Hei 8-171010 discloses a color filter using thermosetting or photocurable ink-jet printing ink containing an acrylamide polymer; Japanese Unexamined Patent Application, First Publication No. Hei 10-17813 discloses a color filter using ink-jet printing ink consisting mainly of a melamine resin, a polycarboxylic acid derivative, and an amine stabilizer; and Japanese Unexamined Patent Application, First Publication No. Hei 7-188596 discloses ink for thermosetting ink-jet recording using a thermosetting resin and a specific amine as a dispersant.
With the recent increase in the size of liquid crystal displays (abbreviated as LCDs), several requirements have arisen for the materials for color filters in the process of manufacturing color LCDs, and examples thereof include heat resistance which is required in the deposition or sputtering processes of a transparent electrode such as ITO and baking process of a color filter, and solvent resistance, which is required in the cleaning process and coating process for LC alignment film. Another requirement is light resistance since the image information is formed by light which is transmitted through the color filter during displaying the image.
Ink-jet printing ink containing an acrylic resin has had the drawback that the resin is liable to decompose when the temperature exceeds 200° C. Although Japanese Unexamined Patent Application, First Publication No. Hei 5-224007 discloses ink-jet printing ink using a thermosetting resin such as a melamine resin for the purpose of improving the heat resistance, this method has the following drawbacks. Since an organic or inorganic acid or an amine or ammonium salt thereof is used in combination with a curing accelerator in the ink used in the method, these compounds remain as impurities in the film, thereby contaminating the sputtering apparatus upon formation of ITO transparent electrodes or such an ink has a short pot life when it is made as an ink in one package type.
In the production of the color filter using the ink-jet printing method, a method using aqueous ink is disclosed in view of environmental issues. Japanese Unexamined Patent Application, First Publication No. Hei 8-319444 discloses a coating composition for a black matrix containing aqueous ink consisting of pigments. Also Japanese Unexamined Patent Application, First Publication No. Hei 10-96810 discloses a method of forming a color filter using hydrophilic ink after exposing a polysilane photosensitive layer to ultraviolet rays to form a hydrophilic latent image.
It has been required to develop a color filter which has excellent heat resistance and does not undergo color changes due to heat, resulting from the increase of the temperature during the deposition of transparent electrodes by vacuum deposition or sputtering process or baking process. In view of the above, it is required to develop a color filter having pixels which is superior in heat resistance and solvent resistance.